Method for the bacterially assisted heap leaching of chalcopyrite

ABSTRACT

A method for the bacterially assisted heap leaching of chalcopyrite, the method characterised by the steps of: providing a chalcopyrite containing ore heap to oxidise sulphide minerals therein, the heap containing and/or being inoculated with a sulphide oxidising bacterial culture that either does not oxidise ferrous to ferric, or is inefficient at doing so; providing at least a first leach solution pond (or other suitable container), from which feed solution is fed to the heap, and which receives leach solution from the heap; and bleeding a portion of the leach solution and passing same to a means for metals recovery.

FIELD OF THE INVENTION

[0001] The present invention relates to a method for the bacteriallyassisted heap leaching of chalcopyrite. More particularly, thebacterially assisted heap leach method of the present invention isintended for use in the recovery of copper in sulphide ores, the copperbeing present in the form of chalcopyrite.

BACKGROUND ART

[0002] The recovery of base metals from sulphide ores by bacteriallyassisted heap leaching is presently restricted to secondary coppersulphide minerals, such as chalcocite and covellite. Chalcopyrite, aprimary copper sulphide mineral, is a notable exception and can notpresently be successfully leached in a heap. The common practice withchalcopyrite ores is to produce a concentrate by froth flotation, forfeeding to a smelter.

[0003] Attempts to leach chalcopyrite in weak to moderately strongsulphuric acid solution, with the addition of ferric as an oxidant,results in the surface passivation of the chalcopyrite, causing thereaction to either stop, or slow down to an unacceptable rate.Similarly, attempts to leach chalcopyrite with bacteria are hindered bythe same surface passivation phenomenon. The mechanism by which thispassivation occurs, and the nature of the passivating layer itself, isnot fully understood.

[0004] The method of the present invention has as one object thereof toovercome the abovementioned problems associated with the prior art, orto at least provide a useful alternative thereto.

[0005] The preceding discussion of the background art is intended tofacilitate an understanding of the present invention only. It should beappreciated that the discussion is not an acknowledgement or admissionthat any of the material referred to was part of the common generalknowledge in Australia as at the priority date of the application.

[0006] Throughout this specification, unless the context requiresotherwise, the word “comprise”, or variations such as “comprises” or“comprising”, will be understood to imply the inclusion of a statedinteger or group of integers but not the exclusion of any other integeror group of integers.

DISCLOSURE OF THE INVENTION

[0007] In accordance with the present invention there is provided amethod for the bacterially assisted heap leaching of chalcopyrite, themethod characterised by the steps of:

[0008] providing a chalcopyrite containing ore heap to oxidise sulphideminerals therein, the heap containing and/or being inoculated with asulphide oxidising bacterial culture that either does not oxidiseferrous to ferric, or is inefficient at doing so;

[0009] providing at least a first leach solution pond (or other suitablecontainer), from which feed solution is fed to the heap, and whichreceives leach solution from the heap; and

[0010] bleeding a portion of the leach solution and passing same to ameans for metals recovery.

[0011] Preferably, the first leach solution pond is maintained with alow ferric concentration relative to that of ferrous.

[0012] Preferably, the first leach solution pond is maintained with anoxidation reduction potential of below 500 mV relative to Ag/AgCl₂standard reference.

[0013] Still preferably, the first leach solution pond is maintainedsuch that the prevailing chemical conditions are conducive to leachingthe chalcopyrite whilst being non-conducive to surface passivation.

[0014] Preferably, the ore heap is aerated at or near a base thereof.

[0015] The oxidation of the chalcopyrite is preferably achieved throughthe action of chemolithotrophic bacteria.

[0016] The method of the present invention may additionally compriseproviding a biological contactor inoculated with ferrous oxidisingbacteria and a second leach solution pond from which leach solution isfed to the biological contactor and which receives leach solution fromthe biological contactor.

[0017] Preferably, leach solution from the first leach pond is able tobe fed to the biological contactor.

[0018] Still preferably, leach solution is able to be fed from thesecond leach pond to the first leach pond, whereby the level of ferricand/or the pH value in the first leach pond may be controlled to a largeextent.

[0019] Still further preferably, leach solution is bled from thebiological contactor for passing to a means for metals recovery, thelevels of ferric therein facilitating metal recovery.

[0020] The biological contactor may be provided in the form of a secondheap. The second heap is preferably formed of relatively inert wasterock inoculated with ferrous oxidising bacteria.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will now be described, by way of exampleonly, with reference to one embodiment thereof and the accompanyingdrawing:

[0022]FIG. 1 is a schematic representation or flow sheet of a method forthe bacterially assisted heap leaching of chalcopyrite in accordancewith one embodiment of the present invention;

[0023]FIG. 2 is graphical representation of the °/ copper leached in anitric acid leach against crush size for a chalcopyrite containing orein accordance with Example 2; and

[0024]FIG. 3 is a graphical representation of copper recoveries inaccordance with Example 2.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

[0025] In the exemplified embodiment it is assumed that the preferredform of iron in the solution bleed stream to the base metal recoverycircuit is the ferric form. The oxidation of the ferrous to ferric inthe leach solution is achieved by passing same through a biologicalcontactor, in the form of a second heap constructed from barren rock orlow-grade ore.

[0026] In FIG. 1 there is shown a flow sheet for the bacteriallyassisted heap leaching of a whole ore or a fraction thereof, by theaction of chemolithotrophic bacteria, in accordance With the presentinvention.

[0027] A disseminated sulphide ore is stacked in a heap 10 on animpermeable leach pad 12. It is envisaged that the disseminated sulphideore may have undergone one or more pre-treatments, for exampleagglomeration, to improve its permeability, or some form of upgradingstep to improve its base metal content.

[0028] The heap 10 has slotted aeration pipes 14 inserted into a base ofthe heap 10 to provide a source of oxygen and carbon to the bacteriapresent in the disseminated sulphide ore. These bacteria are encouragedto multiply and populate the heap, and consequently oxidise the sulphideminerals.

[0029] It is envisaged that the process of the present invention mayrequire a different bacterial species to populate the ore heap than thatoccurring naturally. Such a species would have to be introduced theretoby way of inoculation. This may be achieved by adding a solutioncontaining the preferred bacteria to the material to be treated before,during and/or after stacking of the heap 10.

[0030] The heap 10 is inoculated with a bacterial culture that does notoxidise ferrous, or is inefficient at doing so, and may include, but isnot limited to, Sulfobacillus thermosulfidooxidans and Thiobacilluscaldus. A preferred bacterial culture has been deposited at theAustralia Government Analytical Laboratories under accession No.NM99/07541.

[0031] A biological contactor, for example a second heap 16 formed of arelatively inert waste rock is provided on a further impermeable leachpad 18. The second heap 16 is similarly provided with slotted aerationpipes 20 near the base thereof. The heap 16 is inoculated with ferrousoxidising bacteria, for example Thiobacillus ferrooxidans, which may ormay not be indigenous to the heap 16.

[0032] Two ponds are provided, including an inert rock pond 40 (a secondpond) and an ore pond 42 (a first pond). The ore pond 42 receives leachsolution from the ore heap 10 by way of gravity feed line 44. The oreheap 10 receives leach solution from the pond 42 by way of the feed line28. Any leach solution not fed to the heap 10 is returned to the pond42.

[0033] The waste rock heap 16 receives leach solution from the inertrock pond 40 by way of the feed line 32. Any leach solution not fed tothe heap 16 is returned to the pond 40. The pond 40 receives leachsolution from the heap 16 by way of gravity feed line 46 in which isprovided a pump 48.

[0034] Overflow from the inert rock pond 40 is directed to the ore pond42 by way of an overflow line 50. Control over the volume of solutiontransferred via line 50, allows for control over the ferric level in theore pond 42.

[0035] Liquor from the ore pond 42 is, in addition to being fed to theheap 10, fed to the heap 16 by way of intermediate line 52 and the feedline 32.

[0036] A bleed line 52 is provided in the gravity feed line 46 from theheap 16 and is used to bleed leach solution now deficient in ferrouswhen compared to the leach solution of pond 42, out of the circuit shownin FIG. 1, and into a means for metals recovery. Conventionalhydrometallurgical means may then be used to recover the base metalsfrom this leach solution.

[0037] The use of separate ponds 40 and 42 allows greater flexibility inthe circuit than possible with a single pond. For example, the two heapsmay be run under differing conditions of pH and ferrous and ferricconcentration. As noted above, control over the volume of solutiontransferred via line 50, allows for control over ferric levels in theore pond 42.

[0038] In this way the ore heap solution pond can be maintained suchthat the prevailing chemical conditions are conducive to leaching thechalcopyrite whilst being non-conducive to surface passivation. Thiswould involve, but not be limited to, maintaining a low ferricconcentration in solution. The ORP (oxidation reduction potential), ofthe solution may, in some circumstances be taken as an indication of therelative concentrations of ferrous and ferric.

[0039] It is envisaged that the heating or cooling of the leach solutionat some point in the flow sheet shown in FIG. 1 may prove advantageous.

[0040] The biological contactor may, it is envisaged, alternately beprovided in the form of a packed column or rotating biologicalcontactor.

[0041] It is further envisaged that the leach solution may preferably berecycled through each heap 10 and 16 more than once in order to increasethe level of dissolved metals. Further, some form of pH control mayprove advantageous.

[0042] The process of the present invention provides for the economicrecovery of copper and other base metal sulphides, for example cobalt,nickel and zinc, from their ores. It is envisaged that the capital andoperating costs of base metals production by the process of the presentinvention will compare favourably with conventional recovery processes.Still further, it is envisaged that the process can be applied tomineral deposits of lower base metal value than would typically beeconomically viable using conventional or prior art methods.

[0043] The present invention will now be described with reference to twoexamples. However, it is to be understood that the following examplesare not to limit the above generality of the invention.

EXAMPLE 1

[0044] Two stirred vessel bacterial leach tests were conducted on 300 gsamples of the same chalcopyrite ore. The ore was finely ground (79%passing 200 mesh) and made up in a slurry with 3 Litres of a solutioncontaining bacteria. Aside from the type of bacteria used in the tests,all other conditions were the same, being a temperature of 45° and a pHof 1.00. The results are shown in Tables 1 and 2.

[0045] In a first test, see Table 1, the bacterial culture containedbacteria indigenous to the ore and having iron oxidising properties. Asa result, ferric was the predominant iron species present during thefirst test and the copper leached after 36 days was only 34.22% of thatinitially present in the ore.

[0046] In a second test, see Table 2, non-iron oxidising bacteria wereused. Consequently, ferrous was the predominant iron species presentduring the leach and after 19 days of leaching, 98.78% of the copper wasleached.

EXAMPLE 2

[0047] Samples of the same chalcopyrite containing ore as used inExample 1 was crushed to various levels of fineness and subjected to aconcentrated nitric acid leach test so as to determine the liberationcharacteristics of the chalcopyrite that is contained in the ore. Theresults of this testing are shown in FIG. 2.

[0048] The results indicate that at a crush size of 100% passing 6.25mm, 50% of the chalcopyrite is exposed and is available for leaching.

[0049] A nominal 5000 tonne heap of the same ore was subsequentlyconstructed, the ore having a crush size of 100% passing 7.5 mm. Theheap was operated in accordance with the present invention as describedhereinabove. The resulting copper leach rate is shown in FIG. 3. Thefinal copper leach extraction is close to that predicted by the nitricacid leach test noted above. This suggests that all, or almost all, ofthe chalcopyrite that was available to the leach, was successfullyleached under these conditions.

[0050] Modifications and variations such as would be apparent to theskilled addressee are considered to fall within the scope of the presentinvention. TABLE 1 Feed: 300 g Desseminated Ore (79% passing 200 mesh) 3L of Indigenous Culture Head Grade: Fe Cu Ni Co S Temperature: 45° C.Operating pH: 1.00 (%) (%) (%) (ppm) (%) 12.5 0.9 0.62 238 4.05 AcidSolutions Extraction ORP DO Added Cum. Fe++ Fe+++ Fe Tot Ni Co Cu Fe NiCo Cu Day mV (mg/L) pH 1 pH 2 (ml) Acid (ml) (g/l) (g/l) (g/l) (mg/L)(mg/L) (mg/L) (%) (%) (%) (%)  0 408 2.19 0.94 31.0 31.0 3.07 1.24 4.31 47 1.81 226 0.00 0.00 0.00 0.00 1 (1 am) 419 3.2 1.07 0.95 8.0 39.0 1(1 pm) 422 1.02 0.95 5.0 44.0  2 432 2.8 1.06 0.96 8.0 52.0  3 452 3.91.02 0.96 5.0 57.0  4 464 3.1 1.06 1.00 3.0 60.0  5 470 3.2 1.03 1.002.0 62.0 2.85 5.38 8.23 207 4.81 286 31.36 25.81 12.61 6.67  6 474 4.01.03 1.00 2.0 64.0  7 475 3.2 1.02 1.02 0.0 64.0  8 474 2.2 1.10 1.006.0 70.0 2.96 6.12 9.08 293 7.32 301 38.16 39.68 23.15 8.33  9 476 2.70.99 0.99 0.0 70.0 10 475 2.7 1.00 1.00 0.0 70.0 11 475 3.5 1.00 1.000.0 70.0 12 476 3.3 1.03 1.00 2.0 72.0 2.79 6.74 9.53 390 9.24 387 41.7655.32 31.22 17.89 13 1.03 1.03 0.0 72.0 14 479 2.5 1.02 1.02 0.0 72.0 15478 4.9 1.04 1.00 3.0 75.0 2.34 7.28 9.62 431 10.08 427 42.48 61.9434.75 22.33 16 480 5.0 1.01 1.01 0.0 75.0 17 484 6.7 1.03 1.00 2.0 77.018 486 5.7 1.04 1.00 2.5 79.5 19 488 4.9 0.98 0.98 0.0 79.5 1.96 8.1410.10 448 18.00 356 46.32 64.68 68.03 14.44 20 491 1.03 1.03 0.0 79.5 21494 4.5 1.03 1.00 2.0 81.5 22 497 0.99 0.99 0.0 81.5 1.73 8.57 10.30 47919.00 393 47.92 69.68 72.23 18.56 23 501 4.5 1.02 1.02 0.0 81.5 24 5043.8 1.01 1.01 0.0 81.5 25 507 3.4 1.00 1.00 0.0 81.5 26 508 1.04 1.003.0 84.5 27 509 4.9 1.01 1.01 0.0 84.5 28 509 5.5 1.02 1.02 0.0 84.5 29509 1.01 1.01 0.0 84.5 1.40 9.10 10.50 555 23.00 450 49.52 81.94 89.0324.89 30 509 1.02 1.02 0.0 84.5 31 508 4.5 1.01 1.01 0.0 84.5 32 508 4.80.99 0.99 0.0 84.5 33 508 4.6 1.05 1.01 3.0 87.5 34 507 4.9 1.04 1.003.0 90.5 35 508 4.9 0.98 0.98 0.0 90.5 36 505 4.7 0.83 0.83 0.0 90.51.12 9.78 10.90 574 22.00 534 52.72 85.00 84.83 34.22

[0051] TABLE 2 Feed: 300 g Desseminated Ore (79% passing 200 mesh) 3 Lof Active Chalcopyrite Culture Head Grade: Fe Cu Ni Co S Temperature:45° C. Operating pH: 1.00 (%) (%) (%) (ppm) (%) 12.5 0.9 0.62 238 4.05Acid Solutions Extraction ORP DO Added Cum. Fe++ Fe+++ Fe Tot Ni Co CuFe Ni Co Cu Day mV (mg/L) pH 1 pH 2 (ml) Acid (ml) (g/l) (g/l) (g/l)(mg/L) (mg/L) (mg/L) (%) (%) (%) (%)  0 392 2.28 0.94 33.0 33.0 3.630.97 4.60  37 1.73 561 0.00 0.00 0.00 0.00 1 (1 am) 409 3.1 1.03 0.956.0 39.0 1 (1 pm) 410 1.02 0.95 6.0 45.0  2 411 2.8 1.04 0.95 7.0 52.0 3 415 3.2 1.01 0.96 3.0 55.0  4 418 3.6 1.08 1.00 5.0 60.0  5 422 3.01.01 1.01 0.0 60.0 5.03 2.49 7.52 122 3.33  624 23.36 13.71 6.72 7.00  6423 4.1 1.02 1.02 0.0 60.0  7 425 3.2 1.04 1.00 3.0 63.0  8 426 2.1 1.061.00 3.0 66.0 5.53 3.01 8.54 155 4.2  669 31.52 19.03 10.38 12.00  9 4272.6 1.01 1.01 0.0 66.0 10 426 2.8 1.04 1.00 2.0 68.0 11 427 2.8 1.011.01 0.0 68.0 12 463 3.1 1.03 1.00 2.0 70.0 6.09 3.07 9.16 214 5.22  98736.48 28.55 14.66 47.33 13 1.03 1.03 0.0 70.0 14 422 2.7 1.05 1.05 0.070.0 15 420 5.5 1.08 1.00 5.0 75.0 7.21 2.57 9.78 243 5.54 1400 41.4433.23 16.01 93.22 16 424 4.8 1.03 1.00 2.0 77.0 17 427 5.4 0.98 0.98 0.077.0 18 427 5.6 1.02 1.00 1.0 78.0 19 430 4.8 1.01 1.01 0.0 78.0 5.874.23 10.10 234 5.96 1450 44.00 31.77 17.77 98.78

1. A method for the bacterially assisted heap leaching of chalcopyrite,the method characterised by the steps of: providing a chalcopyritecontaining ore heap to oxidise sulphide minerals therein, the heapcontaining and/or being inoculated with a sulphide oxidising bacterialculture that either does not oxidise ferrous to ferric, or isinefficient at doing so; providing at least a first leach solution pond(or other suitable container), from which feed solution is fed to theheap, and which receives leach solution from the heap; and bleeding aportion of the leach solution and passing same to a means for metalsrecovery.
 2. A method according to claim 1, characterised in that thefirst leach solution pond is maintained with a low ferric concentrationrelative to that of ferrous.
 3. A method according to claim 1 or 2,characterised in that the first leach solution pond is maintained withan oxidation reduction potential of below 500 mV relative to Ag/AgCl₂standard reference.
 4. A method according to any one of claims 1 to 3,characterised in that the first leach solution pond is maintained suchthat the prevailing chemical conditions are conducive to leaching thechalcopyrite whilst being non-conducive to surface passivation.
 5. Amethod according to any one of the preceding claims, characterised inthat the ore heap is aerated at or near a base thereof.
 6. A methodaccording to any one of the preceding claims, characterised in that theoxidation of the chalcopyrite is achieved through the action ofchemolithotrophic bacteria.
 7. A method according to any one of thepreceding claims, characterised in that the method additionallycomprises providing a biological contactor inoculated with ferrousoxidising bacteria and a second leach solution pond from which leachsolution is fed to the biological contactor and which receives leachsolution from the biological contactor.
 8. A method according to claim7, characterised in that leach solution from the first leach pond isable to be fed to the biological contactor.
 9. A method according toclaim 7 or 8, characterised in that leach solution is able to be fedfrom the second leach pond to the first leach pond, whereby the level offerric and/or the pH value in the first leach pond may be controlled toa large extent.
 10. A method according to any one of claims 7 to 9,characterised in that leach solution is bled from the biologicalcontactor for passing to a means for metals recovery, the levels offerric therein facilitating metal recovery.
 11. A method according toany one of the preceding claims, characterised in that the biologicalcontactor is provided in the form of a second heap.
 12. A methodaccording to claim 11, characterised in that the second heap is formedof relatively inert waste rock inoculated with ferrous oxidisingbacteria.
 13. A method for the bacterially assisted heap leaching ofchalcopyrite substantially as hereinbefore described with reference tothe Examples.
 14. A method for the bacterially assisted heap leaching ofchalcopyrite substantially as hereinbefore described with reference tothe accompanying Figures.